The present invention relates to a network system using an ATM network as a relay network to LANs (Local Area Networks).
In recent years, applied technologies using an ATM (Asynchronous Transfer Mode) have been increasingly developed, and services utilizing the ATM have also been developed and utilized. In particular, when using an ATM network in the case of using Internet, multimedia services according the TCP/IP (Transmission Control Protocol/Internet Protocol) are provided with a proper QOS (Quality of Service). Under such circumstances, some technologies (ATM-LAN) using the ATM network as a relay network to LANs are proposed.
The plurality of LANs are connected through the ATM network and treated as being logically one LAN, in which case the respective LANs are connected by remote bridge (hereinafter simply referred to as xe2x80x9cbridgesxe2x80x9d). A technology of connecting the plurality of LANs through the ATM network used as a relay network has already been proposed in the invention disclosed in Japanese Patent Application Publication No.7-202908 (referred to as a xe2x80x9cpreceding intention (1)xe2x80x9d) and in the invention disclosed in Japanese Patent Application Publication No.8-8917 (referred to as a xe2x80x9csecond preceding invention (2)xe2x80x9d).
FIGS. 25 and 26 are explanatory diagrams showing the preceding invention (1). As illustrated in FIG. 25, LANs 1-3 are connected through bridges A-C to an ATM network. The bridge A is connected to the bridges B and C through a point-to-point transmission PVC (Permanent Virtual Connection) and a point-to-multipoint transmission PVC. Data packets transmitted from a LAN 1 to LANs 2, 3 are transmitted on the above connections in the ATM network ((between the bridges) in such a state that a plurality of ATM cells (hereinafter simply called xe2x80x9ccellsxe2x80x9d) are stored with the data packets.
If a destination physical address (which is also called an MAC (Media Access Control) address) of the packet can be specified, each of the bridges A-C transmits the packets (the cells) to the bridge accommodating a transmission party (LAN) by use of the is point-to-point PVC. On the other hand, if unable to specify the MAC address of the packet (or if broadcasting of the MAC address is designated), each of the bridges A-C transmits the all the packets (the cells) to other bridges by using the point-to-multipoint PVCs.
Further, as shown in FIG. 26, when the plurality of LANs 1-4 are connected through the bridges A-D to the ATM network, the bridges A-D are connected in mesh by the point-to-point PVCs and further connected by the point-to-multipoint PVCs. What is shown as the PVCs in FIG. 26 is, however, only the point-to-multipoint PVCs for connecting the bridge A to other bridges B-d.
The bridge in many cases transfers the packets (frames) received from the LAN to all other bridges (LANs). Therefore, for example, the bridge A shown in FIG. 26 prepares the packets corresponding to the number of other bridges (xe2x80x9c3xe2x80x9d in the example in FIG. 26), then converts the prepared packets into the cells, and transfers the data to the bridges B-D by using the point-to-multipoint PVCs.
Moreover, according to the preceding invention (2), as in the preceding invention (1), the bridges are connected through the point-to-point SVCs (Switched Virtual Connections) and the point-to-multipoint PVCs. In the preceding invention (2), however, the point-to-point SVC is established or disconnected corresponding to a condition of throughput of the ATM network. In the preceding invention (2), resources (e.g., buffer memories for retaining the cells) are thereby effectively utilized.
There arise, however, the following problems inherent in the preceding inventions (1) and (2). To be specific, the point-to-point and point-to-multipoint connections in the preceding invention (1) are the permanent virtual connections. Therefore, these connections occupy the resources of the ATM network at all times regardless of a necessity or non-necessity for transmitting the packets.
This might cause a possibility in which an operational flexibility of the ATM network declines.
Further, according to the preceding invention (1), the bridges are connected through the PVCs. Hence, if a new LAN is connected to the ATM network, a maintenance person of the network must set the connections between a newly installed bridge and other bridges, which is laborious.
On the other hand, in the preceding invention (2), the point-to-point SVC is established in accordance with a necessity for transmitting the packets between the bridges. If a congestion occurs in the ATM network before the SVC is established, however, the resources can not be ensured, resulting in a possibility where the SVC might not be established. Namely, there might be a feasibility in which the packet transmission between the bridges can not be assured. Furthermore, in the preceding invention (2) also, the point-to-multipoint connection is set based on the PVC, and hence the maintenance becomes laborious as in the case of the preceding invention (1).
It is a primary object of the present invention, which overcomes the problems described above, to provide a network system capable of relieving a laborious operation of a maintenance person of an ATM network and enhancing an assurance of a packet transmission in the ATM network.
To accomplish this object, according to a first aspect of the present invention, a network system comprises a ATM network, and a plurality of bridges connected through the ATM network. In this network system, a specified bridge among the plurality of bridges sends a request for setting a switched virtual connection for a point-to-multipoint transmission, towards any one of bridge among other bridges. Each of said other bridges, when receiving the setting request sent from the specified bridge, sets the switched virtual connection for point-to-multipoint transmission between the specified bridge and the other bridge.
According to the first aspect of the present invention, when the bridge is newly connected to the ATM network, this bridge becomes a specified bridge, and the switched virtual connection for point-to-multipoint transmission (SVC) is automatically set between this bridge and other bridge. Consequently, there is relieved a laborious operation by the maintenance person of the network which is concomitant with the new installation of the bridge.
According to a second aspect of the present invention, a network system comprises a ATM network, and a plurality of bridges connected through the ATM network. In this network system, each of the bridges is connected to each of other bridges through a connection for point-to-point transmission. Each of the bridges, if there is an unused connection among the connections accommodated in the bridge, gives the ATM network a rate decreasing message for decreasing a transmission rate of the unused connection. The ATM network, when receiving the rate decreasing message, decreases the transmission rate of the unused connection by releasing resources allocated to the unused connection, and allocates the released resources to a other connection.
According to the second aspect of the present invention, the resources of the unused connection are allocated to a other connection, and hence the resources of the ATM network can be effectively utilized. In this case, the connection is not disconnected and established as done in the prior art, and it is therefore feasible to eliminate such a case that the packets can not be transmitted because of the connection being unable to be established. Namely, an assurance of the packet transmission in the ATM network can be more enhanced. The connection for connecting the bridge equipments to each other may involve the use of the PVC or the SVC.
These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to be accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.